Hydraulic apparatus



0, 1966 D. E. LAMBETH 3,269,122

HYDRAULI C APPARATUS Filed April 15, 1965 2 Sheets-Sheet 1 Daring E. Lambg 'h An-w-mauEv Aug. 30, 1966 D. E. LAMBETH HYDRAULIC APPARATUS 2 Sheets-Sheet 2 Filed April 15, 1965 Iwvawroe Dennis E. Lqmbefh ham V United States Patent 3,269,122 HYDRAULIC APPARATUS Dennis Ernest Lambeth, Uheltenham, England, assignor to Dowty Technical Developments Limited, Cheltenham, England, a British company Filed Apr. 15, 1965, Ser. No. 448,295 Claims priority, application Great Britain, Apr. 18, 1964, 16,184/ 64 8 Claims. (CI. 60-53) This invention relates to a hydraulic apparatus and more particularly to a hydraulic power transmission which comprises a variable positive displacement hydraulic pump in hydraulic connection with a variable positive displacement hydraulic motor, the pump being adapted to receive power from .a power source and the motor being adapted to deliver power to the load, the speed ratio between the pump speed and motor speed being determined by the relative displacement of the pump and the motor.

The present invention is concerned with a hydraulic power transmission having a pump and a motor each of the tilting head kind and each comprising a rotary member secured to a drive shaft and a head tiltable about a tilt axis relatively to the rotary member. The head comprises a frame or casing containing a rotary cylinder block, a rotary drive means between the rotary member and the cylinder block and pistons associated with the cylinder block and arranged for reciprocation during rotation of the rotary member. The tilt angle of the head relatively .to the rotation axis of the rotary member determines the effective stroke of the pistons in their cylinders. A valve means containing a pair of ports is used for the supply and the return flow of liquid to and from the cylinders. A pump or motor of the kind set forth in this paragraph will, for convenience, be referred to hereafter as a tilting head pump unit or a tilting head motor unit.

In accordance with the present invention a hydraulic power transmission comprises a tilting head pump unit in hydraulic connection with a tilting head motor unit, a support carrying the two units and locating the tilt axes and the drive shafts in fixed relative positions in which the tilt axes are parallel to one another, a link of fixed length having a pair of spaced pivots connecting the link respectively to the pump head and to the motor head, the pivots being attached to the head either di rectly or by extensions whereby the spacing for each head between the tilt axis and the pivot axis forms a lever arm, the pivot axes being parallel to the tilt axes, stops or limiting means for the pump head so that the range of permitted angular movement of the pump head includes a position, refer-red to as pump dead centre position, where the pump tilt axis lies in a plane with the pivot axes, this position defining the maximum hydraulic capacity position of themotor, the pivot axes in the pump dead centre position lying one on either side of a plane passing through the tilt axes.

Where the relative spacings between the tilt and pivot axes are such that the two pivot axes may occupy a position in one plane with the motor tilt axis, referred to as the motor dead centre position, the stop or limiting means are preferably so arranged as to prevent the motor from entering the motor dead centre position.

The transmissions in accordance with the invention may be arranged in three basically different forms, as follows:

-(a.) The motor lever arm is shorter than the spacing 3,269,122 Patented August 30, 1966 between the tilt axes and lies at an acute angle to the common plane of the tilt axes in the pump dead centre position,

(-b) The motor lever arm lies at an obtuse angle to the common plane of the tilt axes at pump dead centre position,

(c) The motor lever arm is longer than the spacing between the tilt axes and lies at an acute angle to the common plane of the tilt axes at the pump dead centre position.

In accordance with a further feature of the present in vention, a hydraulic transmission comprises a tilting head pump unit, a tilting head motor unit, a support carrying the two units and locating the tilt axes and the drive shafts in fixed relative positions in which the tilt axes are parallel to one another, a link of fixed length having a pair of spaced pivots connecting the link respectively to the pump head and the motor head, the pivots being attached to the heads either directly or by extensions whereby the spacing for each head between the tilt axis and the pivot axis forms a lever arm, the pivot axes being parallel to the tilt axes and lying one on either side of the plane passing through the tilt axes and the motor arm lying at an acute angle to the plane passing through the tilt axes when the pivot axes and the pump tilt axis lie in one plane, i.e. in the pump dead centre position.

The motor lever arm may either be shorter than or longer than the spacing between the tilt axes.

How the invention can be carried into effect is hereinafter particularly described with reference to the accompanying drawings in which,

FIGURE 1 illustrates one arrangement of the tilt and pivot axes according to the invention,

FIGURES 2 and 3 indicate diagrammatically two difterent forms of transmission based on the axis arrangement of FIGURE 1,

FIGURE 4 illustrates another relative arrangement of pivot and tilt axes according to the invention,

FIGURE 5 indicates diagrammatically one transmission based on the arrangement of FIGURE 4,

FIGURE 6 illustrates a third arrangement of pivot and tilt axes according to the invention,

FIGURE 7 illustrates one transmission based on the axis arrangement of FIGURE 6, and

FIGURE 8 shows by way of example a cross section through a typical tilting head pump or motor unit used in the invention.

Initially reference is made to the tilting head unit illustrated in FIGURE 8. A drive shaft 13 is mounted for rotation within a fixed bearing housing 14 which is adapted by any convenient means to be fixedly secured in its operating position. The drive shaft 13 is integrally formed with a drive flange 15 which bears against a thrust bearing surface '16 formed on the housing 14. A pair of trunnions 17 are formed one on either side of the bearing housing 14, which trunnions are engaged by the arms 8 of a yoke 19. It will be understood that the yoke includes a pair of arms 18 disposed one on either side of the drive flange 15. The base 21 of the yoke 19 comprises a valve plate on which a cylinder block 22 is mounted for rotation. The cylinder block 22 is located in position on the valve plate by means of a fixed axle 23 secured to the valve plate 2 1. Within the cylinder block 22 a number of cylinders 24 are formed whose axes extend parallel to the axis of block rotation. These cylinders are open at the end of the cylinder block facing the drive flange 15. The end of the cylinder block 22 which cooperates with the valve plate 21 is formed with a number of cylinder ports 25 which extend one from each cylinder 24. The ports 25 co-operate with a pair of fixed ports 26 and 27 in the valve plate. Within each cylinder 24 a piston 28 is slidably mounted. Each piston is hollow and includes a connecting rod 29 secured within the hollow portion and capable of limited angular movement in the piston. The connecting rods '29 extend from the pistons and terminate in ball joints 31. Each ball joint 31 is located within a socket member 32 fixed in the drive flange 15. The yoke 19 and cylinder block 22 being pivotally mounted at the trunnions 17 are capable of angular movement about the trunnion axis which is arranged to pass diametrically through the drive flange '15 through a circle on which the centres of the ball joints 31 are located. Assuming that the yoke is so positioned that the rotation axes of the cylinder block 24 and the drive shaft 13 are inclined to one another it will be seen that rotation of the drive shaft and rotation of the cylinder block will cause reciprocation of the pistons 28 within cylinders 24, one complete reciprocation of each piston being effected for each complete revolution of the drive shaft 13. The ports 26 and 27 are so positioned that by rotation of the drive shaft 13 liquid is displaced from one of the ports 26 or 27 and delivered at the other port 26 or 27. Rotational drive of the cylinder block is obtained by virtue of the fact that the connecting rods 29 engage the interior surfaces of their associated pistons 28. The stroke of the pistons 28 within their cylinders is determined by the angular inclination of the rotation axis of the cylinder block 22 to the rotation axis of the drive shaft 13, the greater the inclination the greater the stroke. At the position where the axes of the cylinder block 22 of the drive shaft 13 are aligned the pistons will have no stroke.

Extending from the yoke 19 is a lug '33 at the end of which a pair of swivel joints 34 are located. From the swivel joints 34 a pair of parallel links extend to the corresponding swivel joints of the other tilting head unit of the transmission. In FIGURES 1 to 7 the two parallel links are indicated as a single link 7. The two parallel links perform the hydraulic function of carrying flow and return liquid in between the two tilting head units for the transmission of power (from the pump drive shaft to the motor drive shaft. The links also perform a mechanical function in that they link together the pump and the motor heads for simultaneous displacement adjusting movement.

Throughout the description of FIGURES 1 to 7 like reference numerals will refer to like parts of the transmissions. Referring now to FIGURE 1 the drawing is taken in a plane perpendicular to the four parallel major axes of the transmission which are as follows:

the pump tilt axis PT,

the motor tilt axis MT,

the pump pivot axis PP, and the motor pivot axis MP.

One transmission based on the axis arrangement of FIGURE 1 is diagrammatically illustrated in FIGURE 2. In this figure the pump drive shaft 3 and the pump tilting head 4 together form a tilting head pump unit whilst the motor drive shaft 1 and the motor tilting head 2 together form a tilting head motor unit. The transmission is mounted in a support (not shown), which provides bearing housings for the pump and motor drive shafts 3 and 1 and for the trunnions 5 and 6 of the pump and motor heads. The axes of the trunnions 5 and 6 form the tilt axes of pump and motor heads and are located in a fixed parallel relation in the support. A link 7 of fixed length is pivotally connected between the pivot positions MP and PP, the pivot MP being formed in a lug 8 extending from the motor head and the pivot PP being formed in a lug 9 extending from the pump head. As previously described the pump and motor heads each contain a rotary cylinder barrel having cylinders and connecting rods which are interconnected with the drive shaft such that during rotation of the drive shaft the pistons are reciprocated within their cylinders, the stroke of the pistons being proportional to the angular tilt of the head about the tilt axis. In the case of the motor, the spacing between the tilt axis MT and the pivot axis MP forms the motor lever arm, whilst in the case of the pump the spacing between the tilt axis PT and the pivot axis PP forms the pump lever arm. If reference is made to FIGURE 1 it will be seen that a quadrilateral linkage is formed by the four sides of a quadrilateral whose corners are hinged together at the pivot and tilt axes. The four sides comprise the support between the tilt axes MT and PT, the pump lever arm, the motor lever arm, and the link. As is Well known with a quadrilateral linkage, the sides are movable relatively to one another about their hinge connections without the lengths of the sides being altered, and in the present invention use is made of this property of a quadrilateral linkage in order to control relative angular movement of motor and pump heads 2 and 4. In FIG- URE 1 the motor and pump lever arms are of approximately equal length and are each shorter than the space between the tilt axes. The link is longer than the space tween the tilt axes. In FIGURE 1 the full lines represent the position of the linkage at the pump dead centre position in which the pump lever arm is aligned with the link, i.e. the axes MP, PT, and PP lie in one plane. In this position the motor lever arm is arranged to occupy a position corresponding to a maximum angular inclination to the motor drive shaft 1. This in turn corresponds to maximum displacement per revolution of the motor. In this position it is arranged that the angular position of the pump head corresponds to zero displacement of the pump per revolution. Means such as a servo motor .11 (FIGURE 2) are provided for adjusting the angular position of the pump head 4 about the tilt axis PT and the servo motor 11 is so arranged that it can move the pump head over a limited angular range only, illustrated in FIGURE 1 by dotted lines representing the limits of position of the pump lever arm and the resulting changes in position of the link and the motor lever arm. It will be seen that movement of the pump head in either direction from the pump dead centre position will result in angular movement of the motor head in one direction only which is arranged to cause reduction of motor displacement per revolution.

In operation of the transmission shown in FIGURES 1 and 2 the pump drive shaft 3 is connected to a suitable power source and the motor drive shaft 1 is connected to a suitable load. In the pump dead centre position, as shown in FIGURE 2, it is arranged that the zero displacement position of the pump head corresponds with the pump dead centre position and, therefore, in the position as shown rotation of the pump drive shaft will cause no liquid to be delivered from the pump 4 and the motor shaft 1 will not rotate. By movement of the pump head 4 in one direction, liquid will be delivered in an appropriate direction to the motor to cause it to rotate in one direction. If movement of the pump head were in the reverse direction, the delivery from the pump to the motor would be reversed causing the motor drive shaft 1 to rotate in the opposite direction. One great advantage of the transmission illustrated lies in the fact that the relation between the pump and the motor displacement is non-linear and that movement of the pump head from its zero displacement position will initially cause only very slight reduction of motor displacement. For small pump head angular movements the pressure generated will lie at a maximum and since the motor will remain substantially at maximum displacement a maximum torque will be developed at the motor drive shaft. Large angular movements of the pump head from the zero displacement position will cause substantial reduction of the displacement of the motor head and the motor may be driven at a substantial speed, having regard to the pump speed. I

The important characteristics of the transmission of FIGURES 1 and 2 are, that in the dead centre pump position firstly the two pivot axes MP and PP lie on opposite sides of a plane passing through the two tilt axes MT and PT, and secondly that there is an acute angle between the motor lever arm and the common plane through the tilt axes. Thirdly the motor lever arm is shorter than the spacing between the tilt axes.

Whilst in FIGURE 2 the drive shafts 1 and 3 are indicated as parallel, it is possible on the axis arrangement of FIGURE 1 to propose differing forms of transmission. FIGURE 3 illustrates a further form of transmission in which the motor and pump drive shafts 1 and 3 are at right angles. However, the relative positions of the four axes and the effective quadrilateral linkage is exactly the same as shown in FIGURES 1 and 2, and the operation is also similar.

Reference is now made to FIGURE 4 of the accompanying drawings, which illustrates a further basic quadrilateral linkage arrangement. The characteristic features of the FIGURE 4 arrangement are that the link 7 is considerably longer than the spacing between the tilt axes and that in the pump dead centre position shown in full lines in FIGURE 4 there is an obtuse angle between the motor lever arm and the plane passing through the tilt axes.

FIGURE 5 illustrates one form of transmission which may be based on the axis arrangement of FIGURE 4. In this arrangement the pump and motor drive shafts 3 and 1 are oppositely directed. The operation of the transmission is the same as described for FIGURE 2.

Reference is now made to the axis arrangement shown in FIGURE 6. In this example the motor lever arm is greater than the spacing between the tilt axes and the included angle between the motor lever arm and the common plane through the tilt axes is an acute angle.

FIGURE 7 illustrates a transmission based on the axis arrangement of FIGURE 6. This transmission includes pump and motor drive shafts 1 and 3 inclined to one another. In this transmission the motor lug 8 is of considerable size in order to provide the 10mg motor lever arm necessary.

In all of the transmissions described in FIGURES 2, 3, 5 and 7, the servo motor 11 is so arranged that it will determine the limits of angular movement of the pump head 4 in both the forward and the reverse directions. In modifications of the basic axis arrangement of FIGURES 1, 4 and 6, it might be possible within the limits of movement imposed on the pump head, for movements of the heads and the link to occur which permit the link pivots to lie in one plane with the motor tilt axis. This would give a motor dead centre position which will effectively lock the heads and the link against movement by the single servo-motor 11. Whilst it is desirable to be able to adjust the transmission through its complete range of adjustment, i.e. from maximum forward to maximum reverse pump displacement, by means of one servo motor, it may on occasions be necessary to design a transmission to obtain certain characteristics which require that the transmission should pass through a motor dead centre position. In this case it would be within the scope of the invention to provide a further servo motor acting on the motor head and enengised in conjunction with the pump servo motor to move the transmission through the motor dead centre position.

In the illustrated transmissions, the link 7 in each case may take the form of two hollow parallel links, which in addition to the function of controlling relative movements of pump and motor heads also serve to carry flow and return liquid between the pump and the motor heads. Where such parallel links are provided they may extend one on either side of the pump head from the pump 6 pivot. Where the link solely controls the relative movements of pump and motor heads, the hydraulic connections between pump and motor heads may take any convenient form and may extend for example between the pump and motor head trunnions.

In all of the transmissions shown in. FIGURES 2, 3, 5 and 7, the pump has been arranged to occupy its zero displacement position when in the pump dead centre position. This arrangement need only be used where approximately equal forward and reverse speed ratios are desired through the transmission. If it is desired, for example, that the forward speed ratio should be considerably greater than the reverse speed ratio it might be desirable to arrange that the pump zero displacement position is spaced by a few degrees of angle from the pump dead centre position.

What is claimed is:

1. A hydraulic power transmission comprising a tilting head pump unit in hydraulic connection with a tilting head motor unit, a support carrying the two units and locating the tilt axes and the drive shafts in fixed relative positions in which the tilt axes are parallel to one another, a link of fixed length having a pair of spaced pivots connecting the link respectively to the pump head and to the motor head, the pivots being attached to the heads either directly or by extensions whereby the spacing for each head between the tilt axis and the pivot axis forms a lever arm, the pivot axes being parallel to the tilt axes, stops or limiting means for the pump head so that the range of permitted angular movement of the pump head includes a position, referred to as pump dead centre position, where the pump tilt axis lies in a plane with the pivot axes, this position defining the maximum hydraulic capacity position of the motor, the pivot axes in the pump dead centre position lying one on either side of a plane passing through the tilt axes.

2. A hydraulic power transmission as claimed in claim 1 in which the relative spacings between the tilt and pivot axes are such that the two pivot axes may occupy a position in one plane with the motor tilt axis referred to as the motor dead centre position, the stop means being so arranged as to prevent the motor from entering the motor dead centre position.

3. A hydraulic power transmission as claimed in claim 1 wherein the motor lever arm is shorter than the spacing between the tilt axes and lies at an acute angle to the common plane of the tilt axes in the pump dead centre position.

4. A hydraulic power transmission as claimed in claim 1 wherein the motor lever arm lies at an obtuse angle to the common plane of the tilt axes at the pump dead centre position.

5. A hydraulic power transmission as claimed in claim 1 wherein the motor lever arm is longer than the spacing between the tilt axes and lies at an acute angle to the common plane of the tilt axes at the pump dead centre position.

6. A hydraulic power transmission comprising a tilting head pump unit, a tilting head motor unit, a support carrying the two units and locating the tilt axes and the drive shafts in fixed relative positions in which the tilt axes are parallel to one another, a link of fixed length having a pair of spaced pivots connecting the link respectively to the pump head and the motor head, the pivots being attached to the heads either directly or by extensions whereby the spacing for each head between the tilt axis and the pivot axis forms a lever arm, the pivot axes being parallel to the tilt axes and lying one on either side of the plane passing through the tilt axes and the motor arm lying at an acute angle to the plane passing through the tilt axes when the pivot axes and the pump tilt axis lie in one plane i.e. in the pump dead centre position.

7. A hydraulic power transmission as claimed in claim 6 wherein the motor lever arm is shorter than the spacing between the tilt axes.

2' 8 8. A hydraulic power transmission as claimed in claim 3,143,859 8/1964 Thoma 60-53 6 wherein the motor lever arm is longer than the spacing 3,163,987 1/1965 Dowty et al. 6053 between the tilt axes. 3,213,619 10/1965 Creighton et a1 60-53 References Cited by the Examiner 5 FOREIGN PATENTS 693,320 8/ 1964 Canada. UNITED STATES PATENTS 962,361 7/1964 Great Britain. 3,142,963 8/1964 Thoma 6053 3,142,964 8/1964 Thoma 6053 EDGAR W. GEOGHEGAN, Primary Examiner. 

1. A HYDRAULIC POWER TRANSMISSION COMPRISING A TILTING HEAD PUMP UNIT IN HYDRAULIC CONNECTION WITH A TILTING HEAD MOTOR UNIT, A SUPPORT CARRYING THE TWO UNITS AND LOCATING THE TILT AXES AND THE DRIVE SHAFTS IN FIXED RELATIVE POSITIONS IN WHICH THE TILT AXES ARE PARALLEL TO ONE ANOTHER, A LINK OF FIXED LENGTH HAVING A PAIR OF SPACED PIVOTS CONNECTING THE LINK RESPECTIVELY TO THE PUMP HEAD END TO THE MOTOR HEAD, THE PIVOTS BEING ATTACHED TO THE HEADS EITHER DIRECTLY OR BY EXTENSIONS WHEREBY THE SPACING FOR EACH HEAD BETWEEN THE TILT AXIS AND THE PIVOT AXIS FORMS A LEVER ARM, THE PIVOT AXES BEING PARALLEL TO THE TILT AXES, STOPS OR LIMITING MEANS FOR THE PUMP HEAD SO THAT THE RANGE OF PERMITTED ANGULAR MOVEMENT OF THE PUMP HEAD INCLUDES A POSITION, REFERRED TO AS PUMP DEAD CENTRE POSITION, WHERE THE PUMP TILT AXIS LIES IN A PLANE WITH THE PIVOT AXES, THIS POSITION DEFINING THE MAXIMUM HYDRAULIC CAPACITY POSITION OF THE MOTOR, THE PIVOT AXES IN THE PUMP DEAD CENTRE POSITION LYING ONE ON EITHER SIDE OF A PLANE PASSING THROUGH THE TILT AXES. 